Image processing apparatus and image processing method

ABSTRACT

An image processing apparatus includes: a converting unit configured to convert a color of input image data based on information representing a correspondence between a brightness level and a color, and generate converted image data; and a setting unit configured to set a gradation characteristic of the input image data, wherein the converting unit converts the color of the input image data based on information representing a first correspondence in a case where the gradation characteristic set by the setting unit is a first gradation characteristic, and converts the color of the input image data based on information representing a second correspondence in a case where the gradation characteristic set by the setting unit is a second gradation characteristic.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an image processing apparatus and animage processing method.

Description of the Related Art

In the image production field, opportunities to handle image data havinga wide dynamic range are increasing. The dynamic range is a range ofvalues related to brightness. A wide dynamic range is called “highdynamic range (HDR)”, and a dynamic range that is narrower compared toHDR is called “standard dynamic range (SDR)”. Image data having HDR iscalled “HDR image data”, and image data having SDR is called “SDR imagedata”.

Currently the standardization of HDR image data, which can betransmitted using Serial Digital Interface (SDI) cable, for example, isadvancing. For example, ST 2084, standardized by Society of MotionPicture and Television Engineers (SMPTE), is proposed. A technique todisplay an image based on HDR image data (HDR image) at high brightnessis also proposed.

ST 2084 indicates gradation characteristics based on the visualcharacteristics of the human eye, and defines the brightness of HDRimage data by the absolute brightness. The ST 2084 defines the absolutebrightness up to 10,000 cd/m². However, a general display apparatus candisplay only a several hundred to several thousand cd/m² brightness, andcannot display a 10,000 cd/m² brightness.

Therefore display apparatuses which can set a part of the dynamic rangeof an HDR image data to a range in which the display apparatus canappropriately display (e.g. absolute brightness range up to 1000 cd/m²,absolute brightness range up to 2000 cd/m²) were proposed. Hereafter,this setting function is called the “HDR setting function”, and therange which is set by the HDR setting function is called the “settingHDR”. In the display apparatus having the HDR setting function, an imagebased on the setting HDR is displayed with gradation conforming to thestandard (gradation characteristic) of the HDR image data. For example,if the standard of the HDR image data is ST 2084, an image based on thesetting HDR is displayed with the absolute brightness defined in ST2084. A brightness related value that is greater than the maximum valueof a plurality of brightness related values belonging to the setting HDRis displayed as a blank dot.

As a system of the HDR image data (standard; gradation characteristic),not only the system of defining the brightness of the HDR image data bythe absolute brightness, but also a system of defining the brightness ofthe HDR image data by the relative brightness was proposed.

In such a field of image production, there is need to confirm thebrightness distribution of the input image data. An available assistfunction to confirm the brightness distribution of the input image datais a function to convert the color of the input image data into a colorin accordance with the brightness gradation value of the input imagedata. The conversion of a color can be regarded as “coloration”, andsuch an assist function can be regarded as a “color conversion function”or a “coloration function”. By displaying an image based on the imagedata after colors are converted by the color conversion function, theuser can confirm the brightness gradation values of the input image databy colors.

FIG. 8 is an example of the correspondence between the brightnessgradation value of the input image data and the color after theconversion by the color conversion function. FIG. 8 is a case when thebrightness gradation value of the input image data is a 10-bit value (0to 1023). In the case of FIG. 8, the 6 colors correspond to 6 rangesconstituting the dynamic range (range of brightness gradation values) ofthe input image data respectively.

A technique related to the color conversion function is disclosed inJapanese Patent Application Publication No. 2014-167609, for example. Inthe technique disclosed in Japanese Patent Application Publication No.2014-167609, a zebra pattern is displayed in an image region in whichthe brightness level (brightness gradation value) is at least apredetermined value.

SUMMARY OF THE INVENTION

As mentioned above, in the case of the conventional color conversionfunction, a color of the input image data is converted into a color inaccordance with the brightness gradation value of the input image data.Therefore even if the conventional color conversion function is used,the user cannot recognize the absolute brightness defined by thegradation characteristic of the input image data, the relativebrightness defined by the gradation characteristic of the input imagedata and the like. Further, the user cannot recognize the distributionof a plurality of absolute brightness values which are delimited by 100cd/m², 200 cd/m² and the like.

In some cases, a brightness related value close to the maximum value ofa plurality of brightness related values belonging to HDR may not beused for display, but in the conventional color conversion function,even the brightness related value that is not used for display isincluded in the targets of the color conversion processing (processingusing the color conversion function). As a result, it becomes difficultto confirm the distribution of the brightness related values. A possiblemethod of solving this problem is narrowing the HDR to the setting HDR,and then converting each color of the image data into a color inaccordance with the brightness gradation value of the image data havingthe setting HDR. If this method is used, however, the distribution ofthe brightness related values, which belong to the HDR but not to thesetting HDR, cannot be confirmed.

The present invention in its first aspect provides an image processingapparatus, comprising:

a converting unit configured to convert a color of input image databased on information representing a correspondence between a brightnesslevel and a color, and generate converted image data; and

a setting unit configured to set a gradation characteristic of the inputimage data, wherein

the converting unit

converts the color of the input image data based on informationrepresenting a first correspondence in a case where the gradationcharacteristic set by the setting unit is a first gradationcharacteristic, and

converts the color of the input image data based on informationrepresenting a second correspondence in a case where the gradationcharacteristic set by the setting unit is a second gradationcharacteristic.

The present invention in its second aspect provides an image processingmethod, comprising:

a converting step of converting a color of input image data based oninformation representing a correspondence between a brightness level anda color, and generating converted image data; and

a setting step of setting a gradation characteristic of the input imagedata, wherein

in the converting step

the color of the input image data is converted based on informationrepresenting a first correspondence in a case where the gradationcharacteristic set in the setting step is a first gradationcharacteristic, and

the color of the input image data is converted based on informationrepresenting a second correspondence in a case where the gradationcharacteristic set in the setting step is a second gradationcharacteristic.

The present invention in its third aspect provides a non-transitorycomputer readable medium that stores a program, wherein

the program causes a computer to execute:

a converting step of converting a color of input image data based oninformation representing a correspondence between a brightness level anda color, and generating converted image data; and

a setting step of setting a gradation characteristic of the input imagedata, wherein

in the converting step

the color of the input image data is converted based on informationrepresenting a first correspondence in a case where the gradationcharacteristic set in the setting step is a first gradationcharacteristic, and

the color of the input image data is converted based on informationrepresenting a second correspondence in a case where the gradationcharacteristic set in the setting step is a second gradationcharacteristic.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram depicting an example of a configuration of a displayapparatus according to this embodiment;

FIG. 2A and FIG. 2B are graphs depicting examples of a range conversionprocessing according to this embodiment;

FIG. 3 is a flow chart depicting an example of a processing flow by acolor conversion parameter generating unit according to this embodiment;

FIG. 4A and FIG. 4B are diagrams depicting examples of a correspondence(correspondence of the absolute brightness and the color) according tothis embodiment;

FIG. 5A and FIG. 5B are diagrams depicting an example of a processingresult by the color conversion processing unit according to thisembodiment;

FIG. 6A and FIG. 6B are examples of a correspondence (correspondence ofthe relative brightness and the color) according to this embodiment;

FIG. 7A to FIG. 7C are examples of a correspondence (correspondence ofthe absolute brightness and the color) according to this embodiment; and

FIG. 8 is an example of a correspondence (correspondence of thebrightness gradation value and the color) according to this embodiment.

DESCRIPTION OF THE EMBODIMENTS

An embodiment of the present invention will be described.

In the following, an example of a display apparatus having an imageprocessing apparatus according to this embodiment will be described. Thedisplay apparatus is, for example, a liquid crystal display apparatus,an organic electro luminescence (EL) display apparatus, a plasma displayapparatus, a micro electro mechanical system (MEMS) shutter type displayapparatus or the like.

The image processing apparatus may be an apparatus that is separatedfrom the display apparatus. The image processing apparatus that isseparated from a display apparatus is, for example, a personal computer(PC), a playback system (e.g. Blu-ray player), a server apparatus or thelike.

FIG. 1 is a diagram depicting a configuration example of a displayapparatus 100 according to this embodiment. The display apparatus 100includes an image input unit 101, an image processing unit 102, a colorconversion processing unit 103, a display unit 104, a CPU 105, a userinterface (UI) unit 106, and a color conversion parameter generatingunit 107.

The image input unit 101 acquires image data (input image data), andoutputs the input image data to the image processing unit 102. In thisembodiment, the image input unit 101 acquires the input image data fromoutside the display apparatus 100 (image processing apparatus). Inconcrete terms, the image input unit 101 includes an SDI input terminalconforming to SDI standards, and acquires the SDI signal from outsidethe display apparatus 100 via the SDI input terminal. Then the imageinput unit 101 converts the SDI signal into image data having a dataformat that can be processed onboard the display apparatus 100, andoutputs the converted image data to the image processing unit 102. Inthis embodiment, a gradation value of the input image data is a 10-bitvalue (0 to 1023).

The method of acquiring the input image data is not especially limited.For example, the display apparatus 100 (image processing unit) mayinclude a storage unit which stores the image data, so that the imageinput unit 101 reads the image data (input image data) from the storageunit. The image signal inputted to the image input unit 101 need not bean SDI signal. And the number of bits (bit depth) of the input imagedata may be more or less than 10 bits.

The image processing unit 102 determines the gradation characteristic ofthe input image data (characteristic determination processing), inaccordance with the user operation (instruction from the user) to thedisplay apparatus 100 (image processing apparatus). Here the useroperation is a user operation to specify the gradation characteristic,for example. The image processing unit 102 performs the imageprocessing, based at least on the determined gradation characteristic,on the input image data outputted from the image input unit 101. Therebythe processing image data is generated. Then the image processing unit102 outputs this processing image data to the color conversionprocessing unit 103. The gradation characteristic is a characteristicrelated to the correspondence between the pre-converted gradation valueand the converted gradation value in the gradation conversionprocessing, to convert the gradation value of the image data, forexample. In this embodiment, one of the three types of gradationcharacteristics: gamma 2.2, SMPTE ST 2084 (perceptual quantization(PQ)); and Log, is determined as the gradation characteristic of theinput image data. The corresponding gradation characteristic is notlimited to the above mentioned gradation characteristic. For example,Hybrid Log-Gamma (HLG) specified in ARIB STD-B67, may be used. In thefollowing description, “the gradation characteristic is ST 2084” meansthat the gradation characteristic is the PQ defined in SMPTE ST 2084.

A wide dynamic range is called the “high dynamic range (HDR)”, and adynamic range, which is narrower than the HDR, is called the “standarddynamic range (SDR)”. The dynamic range is a range of values related tothe brightness (brightness level). The brightness related value(brightness level) is, for example, a brightness gradation value (Yvalue), and absolute brightness, a relative brightness or the like.Image data having HDR is called “HDR image data”, and image data havingSDR is called “SDR image data”. Gamma 2.2 is the gradationcharacteristic corresponding to SDR, and ST 2084 and Log are thegradation characteristics corresponding to HDR.

ST 2084 is a gradation characteristic when the absolute brightnesscorresponds to the pixel value (gradation value) of the input imagedata, and Log is a gradation characteristic when the relative brightness(relative brightness level) corresponds to the pixel value of the inputimage data. In other words, ST 2084 is a gradation characteristic whenthe brightness of the input image data is defined by the absolutebrightness, and Log is a gradation characteristic when the brightness ofthe input image data is defined by the relative brightness. HLG is agradation characteristic when the brightness of the input image data isdefined by the relative brightness. The correspondence of the relativebrightness to the pixel value can be regarded as the indirectcorrespondence of the brightness level to the pixel value. If HLG isused as the gradation characteristic, processing the same as the casewhen the gradation characteristic is Log is performed.

In the case when the brightness (absolute brightness or relativebrightness) corresponds to the pixel value, as in the case of ST 2084and Log, a characteristic related to the correspondence between thepixel value of the image data and the brightness of the image data canbe used as the gradation characteristic. In concrete terms, as theinformation on the gradation characteristic, the information thatrepresents the correspondence between the pixel value of the image dataand the brightness of the image data (e.g. function, table) can be used.This information is called “electro-optical transfer function (EOTF)”.

The image processing performed by the image processing unit 102 includesthe gradation conversion processing and the range conversion processing.The gradation conversion processing is a processing to convert thegradation value of the input image data in accordance with thedetermined gradation characteristic. For example, in the gradationconversion processing, the gradation value of the input image data isconverted using a predetermined look up table (LUT), which correspondsto the determined gradation characteristic. In the gradation conversionprocessing, a one-dimensional LUT (1-DLUT) or the like is used as thepredetermined LUT. Instead of the predetermined LUT, a predeterminedfunction may be used.

The range conversion processing is a processing to correct the inputimage data (gradation value of the input image data), so that at least apart of the dynamic range of the input image data can be appropriatelydisplayed. In this embodiment, the range conversion processing isperformed in the case when the gradation characteristic of the inputimage data is ST 2084, and when the gradation characteristic of theinput image data is Log.

In this embodiment, the image processing unit 102 determines at least apart of the dynamic range of the input image data as the specifieddisplay range, in accordance with the user operation to the displayapparatus 100 (image processing apparatus). In concrete terms, the imageprocessing unit 102 determines the maximum value of a plurality ofbrightness related values belonging to the specified display rangeaccording to the user operation (first threshold determinationprocessing). Thereby the range, from the minimum value of a plurality ofbrightness related values belonging to the dynamic range of the inputimage data, to the determined maximum value (maximum value of aplurality of brightness related values belonging to the specifieddisplay range), is used as the specified display range. Then in therange conversion processing, the input image data is corrected based onthe specified display range (determined maximum value). Thereby when thelater mentioned color conversion processing is not performed, thespecified display range is displayed at a gradation conforming to thestandard (gradation characteristic) of the input image data. Then eachover-range pixel is displayed at a predetermined color. An over-rangepixel refers to a pixel which has a brightness related value that ishigher (greater) than the maximum value of the plurality of brightnessrelated values belonging to the specified display range. For example, apixel having such a brightness related value is displayed as white(blank dot).

Here a case when the gradation characteristic of the input image data isST 2084, and the maximum brightness of a plurality of absolutebrightness values belonging to the specified display range is 1000 cd/m²is considered. ST 2084 defines the absolute brightness in a 0 to 10,000cd/ms² range. This embodiment can implement only a 0 to 1000 cd/m²display brightness (brightness on the screen) In this case, the inputimage data is corrected so that an absolute brightness not higher than1000 cd/m² (absolute brightness defined in ST 2084) is directlydisplayed, and an absolute brightness higher than 1000 cd/m2 isdisplayed at 1000 cd/m² (FIG. 2A). Next a case when the gradationcharacteristic of the input image data is ST 2084, and when the maximumbrightness value of a plurality of absolute brightness values belongingto the specified display range is 10,000 cd/m² is considered. In thiscase, the input image data is corrected and displayed so that the range,including the absolute brightness in a 0 to 10,000 cd/m² range (absolutebrightness defined in ST 2084), is compressed to the range including thedisplay brightness in a 0 to 1000 cd/m² range (FIG. 2B).

The method for determining the gradation characteristic of the inputimage data is not especially limited. For example, the characteristicinformation related to the gradation characteristic of the input imagedata may be included in the meta data attached to the input image data.Then the image processing unit 102 may determine the gradationcharacteristic of the input image data in accordance with thecharacteristic information acquired from the meta data of the inputimage data (characteristic determination processing). The imageprocessing unit 102 may automatically determine the gradationcharacteristic of the input image data in accordance with the type ofthe input image data (e.g. medical image, illustration image, landscapeimage). The image processing unit 102 may automatically determine thegradation characteristic of the input image data in accordance with theoperating environment of the display apparatus 100 (image processingapparatus). The operating environment of the display apparatus 100includes the temperature of the display apparatus 100, the ambientbrightness of the display apparatus 100 and the like.

For the characteristic information, information representing thecorrespondence between the pre-conversion gradation value and theconverted gradation value in the gradation conversion processing, forexample, may be used. Also for the characteristic information,information representing the correspondence between the pre-conversiongradation value and the converted gradation value, in the gradationconversion processing already performed on the input image data, may beused. If the brightness (absolute brightness or relative brightness) iscorresponded to the pixel value, such as ST 2084 and Log, theinformation representing the correspondence between the pixel value ofthe image data and the brightness of the image data, may be used as thecharacteristic information. In EOTF, the input value is a pixel value,and the output value is the brightness. On the other hand, information,in which the input value is the brightness and the output value is thepixel value (e.g. function, table), is called “opto-electronic transferfunction (OETF)”. If the brightness is corresponded to the pixel value,then EOTF, OETF or the like may be used as the characteristicinformation.

The method of determining the specified display range (maximum value ofa plurality of brightness related values belonging to the specifieddisplay range) is not especially limited. For example, the rangeinformation, to indicate the specified display range, may be included inthe meta data of the input image data. Then the image processing unit102 may determine the specified display range in accordance with therange information. Further, the image processing unit 102 mayautomatically determine the specified display range in accordance withthe type of the input image data. The image processing unit 102 mayautomatically determine the specified display range in accordance withthe operating environment of the display apparatus 100 (image processingapparatus).

The gradation characteristic of the input image data, the dynamic rangeof the input image data, the range of the display brightness, the imageprocessing performed by the image processing unit 102, the brightnessrelated value and the like are not especially limited. For example,various gradation characteristics that are proposed may be used as thegradation characteristics of the input image data. The range of thedisplay brightness may be wider or narrower than 0 to 1000 cd/m² range.The range conversion processing may be omitted in at least one of thecases when the gradation characteristic of the input image data is ST2084, and when the gradation characteristic of the input image data isLog. The range conversion processing may be performed in the case whenthe gradation characteristic of the input image data is gamma 2.2. Theimage processing unit 102 may omit the gradation conversion processing.For the input image data, the image data after the image processing unit102 performed gradation conversion processing may be acquired.

The color conversion processing unit 103 converts the colors of theprocessing image data outputted from the image processing unit 102 usinga color conversion parameter generated by the color conversion parametergenerating unit 107 (color conversion processing). Thereby the displayimage data (converted image data) is generated. The color conversionprocessing unit 103 outputs the display image data to the display unit104. The color conversion can be regarded as “coloration”, and the colorconversion processing can be regarded as “coloration processing”. Thecolor conversion parameter is, for example, a table that indicates theconverted color (color after conversion in the color conversionprocessing) for each pixel of the processing image data. The colorconversion processing unit 103 may generate the display image data byperforming the color conversion processing on the input image datainstead of the processing image data.

The display unit 104 displays an image on the screen based on thedisplay image data outputted from the color conversion processing unit103. For the display unit 104, a spontaneous light emitting type displaypanel, a combination of a light emitting unit and a modulation panel orthe like can be used. The spontaneous light emitting type display paneldisplays an image on the screen by emitting light based on the displayimage data. The light emitting unit irradiates light to the modulationpanel. Then the modulation panel displays an image on the screen bymodulating (e.g. transmitting, reflecting) the light emitted from thelight emitting unit, based on the display image data. The light emission(e.g. emission brightness, emission color) of the light emitting unitmay be controlled based on the display image data. In the case of thetransmission type liquid crystal display apparatus, the light emittingunit is called a “backlight unit”, and the modulation panel is called a“liquid crystal panel”. The backlight unit irradiates light to the rearface of the liquid crystal panel. The liquid crystal panel displays animage on the screen by transmitting the light emitted from the backlightunit.

The CPU 105 controls the operation of the display apparatus 100 (eachfunction unit of the display apparatus 100). For example, the displayapparatus 100 includes a storage unit (e.g. non-volatile memory) whichstores a program, and the CPU 105 reads the program from the storageunit and executes the program, whereby the operation of the displayapparatus 100 is controlled.

The UI unit 106 receives the user operation that the user performed tothe display apparatus 100 (image processing apparatus). Then the UI unit106 outputs the operation signal received in accordance with the useroperation to other functional units (e.g. image processing unit 102,color conversion processing unit 103, CPU 105, color conversionparameter generating unit 107) of the display apparatus 100. The UI unit106 is, for example, buttons disposed on the display apparatus 100, atouch panel disposed on the display unit 104 or the like. A control unitthat is detachable from the display apparatus 100 (e.g. controller,keyboard, mouse) may be used as the UI unit 106.

The UI unit 106 is used for such user operations as the characteristicsetting operation, the range setting operation, and the color conversionsetting operation. The characteristic setting operation is a useroperation to determine the gradation characteristic of the input imagedata. For example, the characteristic setting operation is a useroperation to specify the gradation characteristic, a user operation tospecify the operation mode of the display apparatus 100 (imageprocessing apparatus) and the like. The range setting operation is auser operation to determine the specified display range. For example,the range setting operation is a user operation to specify the specifieddisplay range, a user operation to specify the maximum value of aplurality of brightness related values belonging to the specifieddisplay range, a user operation to specify the operation mode of thedisplay apparatus 100 and the like. The color conversion settingoperation is a user operation to determine whether the color conversionprocessing is executed. For example, the color conversion settingoperation is a user operation to determine whether or not the colorconversion processing is executed, a user operation to specify theoperation mode of the display apparatus 100 and the like.

In this embodiment, the setting to specify whether the color conversionprocessing is called a “false color setting”. The color conversionparameter generating unit 107 switches the state of the false colorsetting between the ON state and the OFF state in accordance with thecolor conversion setting operation. The ON state is a state to executethe color conversion processing, and the OFF state is a state to notexecute the color conversion processing. Selecting the state of thefalse color setting determines whether the color conversion processingis executed or not. For example, the color conversion processing unit103, the color conversion parameter generating unit 107, or both ofthese units select the state of the false color setting in accordancewith the color conversion setting operation.

In the range setting operation to specify the maximum value of aplurality of brightness related values belonging to the specifieddisplay range, the type of the brightness related values is notespecially limited. For example, the user operation, to specify themaximum value using the brightness gradation value, may be performed asthe range setting operation, regardless the gradation characteristic ofthe input image data. However, in terms of convenience, it is preferablethat the user operation to specify a type of brightness gradation valuein accordance with the gradation characteristic of the input image datais performed as the range setting operation. For example, if thegradation characteristic of the input image data is ST 2084, it ispreferable that the user operation to specify the absolute brightness isperformed as the range setting operation. If the gradationcharacteristic of the input image data is Log, it is preferable that theuser operation to specify the relative brightness is performed as therange setting operation.

The color conversion parameter generating unit 107 generates the colorconversion parameter based on the information representing thecorrespondence between the brightness related value (brightness level)of the input image data and the converted color of the color conversionprocessing, and the input image data. For example, as mentioned above,the table indicating the converted color of each pixel is generated asthe color conversion parameter. Then the color conversion parametergenerating unit 107 outputs the generated color conversion parameter tothe color conversion processing unit 103. Thereby in the colorconversion processing, each color of the processing image data isconverted based on the correspondence. In this embodiment, the colorconversion parameter generating unit 107 uses the correspondence inaccordance with the determined gradation characteristic of the inputimage data. Hence the brightness distribution of the input image datacan be displayed more appropriately. For example, if the gradationcharacteristic of the input image data is gamma 2.2, the correspondenceof the converted color and the brightness generation value of the inputimage data is used. If the gradation characteristic of the input imagedata is ST 2084, the correspondence of the converted color and theabsolute value of the input image data is used. If the gradationcharacteristic of the input image data is Log, the correspondence of theconverted color and the relative brightness of the input image data isused. In other words, the color conversion parameter generating unit 107switches the correspondence between the brightness level and theconverted color in accordance with the gradation characteristic.

The gradation characteristic of the input image data is determined bythe color conversion parameter generating unit 107. Both the imageprocessing unit 102 and the color conversion parameter generating unit107 may determine the gradation characteristic of the input image datarespectively. In the same manner, the specified display range (maximumvalue of a plurality of brightness related values belonging to thespecified display range) may be determined by the color conversionparameter generating unit 107. Both the image processing unit 102 andthe color conversion parameter generating unit 107 may determine thespecified display range respectively.

An example of the processing flow by the color conversion parametergenerating unit 107 will be described with reference to the flow chartin FIG. 3.

First in S101, the color conversion parameter generating unit 107determines whether the state of the false color setting is the ON state.If the state of the false color setting is the OFF state (S101: NO),processing advances to S102, and if the state of the false color settingis the ON state (S101: YES), processing advances to S103.

In S102, the color conversion parameter generating unit 107 selects “nocoloration” as the pattern of the correspondence between the brightnessrelated value of the input image data and the converted color.

In S103, the color conversion parameter generating unit 107 determineswhether the gradation characteristic of the input image data correspondsto HDR. If the gradation characteristic of the input image data does notcorrespond to HDR (S103: NO), processing advances to S107, and if thegradation characteristic of the input image data corresponds to HDR(S103: YES), processing advances to S104. In concrete terms, if thegradation characteristic of the input image data is gamma 2.2, it isdetermined that the gradation characteristic of the input image datacorresponds to SDR, and processing advances to S107. If the gradationcharacteristic of the input image data is ST 2084 or Log, it isdetermined that the gradation characteristic of the input image datacorresponds to HDR, and processing advances to S104.

In S107, the color conversion parameter generating unit 107 selects“pattern C” as the pattern of the correspondence between the brightnessrelated value of the input image data and the converted color.

In S104, the color conversion parameter generating unit 107 determineswhether the absolute brightness is defined in the gradationcharacteristic of the input image data. If the absolute brightness isdefined in the gradation characteristic of the input image data (S104:YES), processing advances to S105. If the absolute brightness is notdefined in the gradation characteristic of the input image data, but therelative brightness is defined in the gradation characteristic of theinput image data (S104: NO), processing advances to S106. In concreteterms, if the gradation characteristic of the input image data is ST2084, processing advances to S105, and if the gradation characteristicof the input image data is Log, processing advances to S106.

In S105, the color conversion parameter generating unit 107 selects“pattern A” as the pattern of the correspondence between the brightnessrelated value of the input image data and the converted color. In S106,the color conversion parameter generating unit 107 selects “pattern B”as the pattern of the correspondence between the brightness relatedvalue of the input image data and the converted color.

If “no coloration” is selected, the color conversion parametergenerating unit 107 generates a color conversion parameter to notconvert the color of the processing image data. As a result, in thecolor conversion processing unit 103, the display image data, which isthe same as the processing image data, is generated by the colorconversion processing. The color conversion parameter to not convert thecolor of the processing image data can be regarded as a “colorconversion parameter of which converted color is the same as thepre-conversion color”. If the state of the false color setting is theOFF state, the generation of the color conversion parameter may beomitted. Then the color conversion processing unit 103 may omit thecolor conversion processing, and output the processing image data as thedisplay image data.

In this embodiment, the color of each over-range pixel is converted intoa predetermined color (e.g. white) by the image processing of the imageprocessing unit 102. An over-range pixel refers to a pixel which has abrightness related value that is higher (greater) than the maximum valueof a plurality of brightness related values belonging to the specifieddisplay range. If “no coloration” is selected, the color of theprocessing image data is not converted, and the color of the over-rangepixel is maintained at the predetermined color. If one of pattern A,pattern B and pattern C is selected, on the other hand, the color of theprocessing image data is converted based on the correspondence betweenthe brightness related value of the input image data and the convertedcolor. Therefore the color of the over-range pixel is also convertedinto a color based on the correspondence between the brightness relatedvalue of the input image data and the converted color.

If the pattern A is selected, the color conversion parameter generatingunit 107 determines a correspondence depicted in FIG. 4A or FIG. 4B inaccordance with the specified display range (maximum brightness value ofa plurality of absolute brightness values belonging to the specifieddisplay range).

FIG. 4A is a case when the maximum brightness value of a plurality ofabsolute brightness values belonging to the specified display range is10,000 cd/m². In other words, in the case of FIG. 4A, the specifieddisplay range includes all the absolute brightness values in a 0 to10,000 cd/m² range defined by ST 2084.

In the correspondence in FIG. 4A, a plurality of converted colors arecorresponded to a plurality of ranges (color conversion ranges) of theabsolute brightness respectively. For example, a monochrome color (gray)corresponds to the color conversion range to which the 95 to 105 cd/m²absolute brightness belongs. Therefore the colors in the portions(pixels) which has a 95 to 105 cd/m² absolute brightness are convertedinto a monochrome color. Green is corresponded to the color conversionrange to which the 995 to 1005 cd/m² absolute brightness belongs.Further, in the correspondence in FIG. 4A, a plurality of colorconversion ranges are separated from each other, and a range, to which aconverted color is not corresponded (non-color conversion range), existsbetween the two color conversion ranges. In the color conversionprocessing, colors of the pixels having an absolute brightness belongingto the non-color conversion range are not converted.

By using the correspondence in FIG. 4A, the distribution of the absolutebrightness belonging to each color conversion range is displayed ascolor. As mentioned above, in the case of the correspondence in FIG. 4A,the plurality of color conversion ranges are separated from each other.Therefore the distribution of the absolute brightness belonging to thecolor conversion range is displayed as a color line.

FIG. 4B is a case when the maximum brightness value of a plurality ofabsolute brightness values belonging to the specified display range is1500 cd/m². In other words, in the case of FIG. 4B, the specifieddisplay range includes a 0 to 1500 cd/m² absolute brightness, and doesnot include an absolute brightness exceeding 1500 cd/m².

In the correspondence in FIG. 4B, the same setting (color conversionrange, non-color conversion range, correspondence between colorconversion range and converted color) as FIG. 4A is performed for thespecified display range. Therefore if the correspondence in FIG. 4B isused, the same result as the case of using the correspondence in FIG. 4Ais acquired as the result of the color conversion processing for pixelshaving the absolute brightness values belonging to the specified displayrange.

Further, in the correspondence in FIG. 4B, a color that is differentfrom the plurality of converted colors, which correspond to theplurality of color conversion ranges respectively, is corresponded tothe non-specified display range. In concrete terms, red is correspondedto the non-specified display range. Therefore the color of a pixelhaving the absolute brightness belonging to the non-specified displayrange is converted to red by the color conversion processing. Thenon-specified display range is a range outside the specified displayrange. In the case of FIG. 4B, the non-specified display range is arange of which absolute brightness value is higher than 1500 cd/m²(maximum brightness value of a plurality of absolute brightness valuesbelonging to the specified display range).

If the pattern A is selected in this way, the correspondence in whichthe converted color is corresponded to the absolute brightness is used,and color conversion processing is performed based on the absolutebrightness. Thereby the absolute brightness (distribution of absolutebrightness) of the input image data can be appropriately displayed bycolors. As a result, the user can easily recognize the absolutebrightness of the input image data by colors. For example, in the caseof FIG. 4A and FIG. 4B, the absolute brightness at the center of thecolor conversion range has a round number value (e.g. 100 cd/m², 200cd/m², 400 cd/m², 1000 cd/m², 2000 cd/m², 4000 cd/m²). Therefore anabsolute brightness having a round number value can be appropriatelydisplayed by colors. As a result, the user can easily recognize theabsolute brightness having a round number value by colors. 100 cd/m²,200 cd/m², 400 cd/m², 1000 cd/m², 2000 cd/m², 4000 cd/m² can be regardedas a plurality of boundaries of a plurality of sub-ranges constitutingthe range of the possible absolute brightness of the input image data.The plurality of color conversion ranges can be regarded as a pluralityof boundary ranges which includes a plurality of boundariesrespectively.

In the correspondences in FIG. 4A and FIG. 4B, a plurality of colorconversion regions are separated from each other, and the distributionof the absolute brightness values belonging to the color conversionrange is displayed as a contour line. Therefore for the image region inthe non-color conversion range, the user can confirm the processingimage (image represented by the processing image data). In other words,the user can confirm the brightness distribution and the processingimage simultaneously.

A converted color that is different from the plurality of convertedcolors, corresponding to the plurality of color conversion rangesrespectively, is corresponded to the non-specified display range.Therefore the image region in the non-specified display range isdisplayed with a color that is different from the colors in the imageregions in the color conversion ranges. Thereby the user can discern theimage region in the non-specified display range and the image region inthe color conversion range.

In the non-specified display range, the brightness of the convertedcolor may continuously change in accordance with the continuous changeof the absolute brightness (brightness related values). Then the colorof each pixel having the absolute brightness value belonging to thenon-specified display range is converted into a color of whichbrightness continuously changes in accordance with the continuous changeof the absolute brightness. As a result, in the image region in thenon-specified display range, gradation display is performed as thedisplay of the converted color, where the brightness of the convertedcolor continuously changes in accordance with the continuous change ofthe absolute brightness. According to this gradation display, the usercan easily recognize the distribution of the absolute brightness in theimage region that is within the non-specified display range.

The color conversion range in FIG. 4A and FIG. 4B has a 10 cd/m² width,but the position of the color conversion range, the width of each colorconversion range, the number of color conversion ranges and the like arenot especially limited. Each color that is corresponded to the colorconversion range, the non-specified display range or the like is notespecially limited either. However it is preferable that a color whichis not used for the other color conversion processing is used as theconverted color.

If a pixel having an absolute brightness value belonging to the colorconversion range is not included in the input image data, the conversioninto a color corresponding to this color conversion range is notperformed. Therefore it is preferable that the color conversionparameter generating unit 107 determines a plurality of color conversionranges, so that the number of pixels having a brightness related valuebelonging to the color conversion range in the input image data is atleast a predetermined number for each of the plurality of colorconversion ranges. For example, it is preferable that the colorconversion parameter generating unit 107 adjusts at least one of theinitial values of the center of the color conversion range, the width ofthe color conversion range and the like, so that the number of pixelshaving a brightness value belonging to the color conversion rangebecomes at least a predetermined number.

In some cases, a plurality of image regions, of which converted colorsare the same and of which the respective size is a predetermined size orless, may have scattered like image noise (FIG. 5A). Therefore it ispreferable that the color conversion processing unit 103 furtherconverts the colors of the image regions among a plurality of imageregions, so that the color of the linear image region connecting aplurality of image regions having image noise becomes the same color asthe converted color of this plurality of image regions (FIG. 5B). InFIG. 5A, a plurality of scattered pixels 301 are a plurality of pixelsconverted into a same color by the color conversion processing. Byfurther converting the color of the pixels among the plurality of pixels301, a noise-like display can be suppressed, and the linear region(linear image region) 302 in FIG. 5B can be displayed as an image regionhaving the same color as the pixel 301. The predetermined size may beone pixel size, or may be a size of a plurality of pixels.

If the pattern B is selected, the color conversion parameter generatingunit 107 determines the correspondence depicted in FIG. 6A or FIG. 6B inaccordance with the specified display range (maximum brightness value ofa plurality of relative brightness values belonging to the specifieddisplay range).

FIG. 6A is an example when the maximum brightness value of a pluralityof relative brightness values belonging to the specified display rangeis 1600%. In Log, the relative brightness in the 0% to 1600% range isdefined. In other words, in the case of FIG. 6A, the specified displayrange includes all the relative brightness values in the 0% to 1600%range defined in Log.

In the correspondence in FIG. 6A, a plurality of converted colorscorrespond to a plurality of ranges (color conversion ranges) of therelative brightness respectively. For example, a monochrome color iscorresponded to the color conversion range to which the relativebrightness values in a 0% to 100% range belong. In other words, amonochrome color is corresponded to the range of a relative brightnessthat is 100% or less (threshold or less). And green is corresponded tothe color conversion range to which the relative brightness values in a400% to 800% range belong.

FIG. 6B is an example when the maximum brightness value of a pluralityof relative brightness values belonging to the specified display rangeis 400%. In other words, in the case of FIG. 6B, the specified displayrange includes relative brightness values in a 0% to 400% range, anddoes not include a relative brightness values higher than 400%. In thecorrespondence in FIG. 6B, a converted color, which is different fromthe plurality of converted colors corresponding to the plurality ofcolor conversion ranges respectively, is corresponded to thenon-specified display range. In concrete terms, red is corresponded tothe non-specified display range. Therefore the color of the pixel havingthe absolute brightness value belonging to the non-specified displayrange is converted into red by the color conversion processing. In thecase of FIG. 6B, the non-specified display range is a range of whichrelative brightness is higher than 400% (maximum brightness value of aplurality of relative brightness values belonging to the specifieddisplay range).

If the pattern A is selected, the position (center) of the colorconversion range is fixed, regardless the specified display range, asillustrated in FIG. 4A and FIG. 4B. The number of color conversionranges changes in accordance with the specified display range. On theother hand, even if the color of the relative brightness changesdepending on the specified display range, the user can easily recognizethe relative brightness. Therefore, as illustrated in FIG. 6A and FIG.6B, if the pattern B is selected, the color conversion parametergenerating unit 107 changes at least the positions of the colorconversion ranges in accordance with the specified display range(maximum brightness value of a plurality of relative brightness valuesbelonging to the specified display range). In the case of FIG. 6A andFIG. 6B, the positions of the color conversion ranges and the width ofeach color conversion range are changed in accordance with the specifieddisplay range, so that the number of the plurality of the colorconversion ranges, the relationship between the plurality of colorconversion ranges and the plurality of converted colors and the like aremaintained. In other words, in the case of FIG. 6A and FIG. 6B, theplurality of color conversion ranges are generally compressed orexpanded in accordance with the specified display range.

In this way, if the pattern B is selected, the correspondence of therelative brightness is used, and the color conversion processing isperformed based on the relative brightness. Thereby the relativebrightness (distribution of the relative brightness) of the input imagedata can be appropriately displayed by colors. As a result, the user caneasily recognize the relative brightness of the input image data bycolors. In this embodiment, the number of the plurality of colorconversion ranges, the relationship between a plurality of colorconversion ranges and a plurality of colors and the like are maintained,hence the relative brightness can be more appropriately displayed, andthe user can more clearly recognize the relative brightness. Further, inthe image region of the non-specified display range, a color that isdifferent from those in the image regions of the color conversion rangesis displayed. Thereby the user can easily discern the image region ofthe non-specified display range and the image region of the colorconversion range.

In a range (at least one of the color conversion range and thenon-specified display range), the brightness of the converted color maycontinuously change in accordance with the continuous change of therelative brightness (brightness related values). Then in the imageregion in this range, gradation display can be performed as the displayof the converted colors, such that the brightness of the convertedcolors continuously change in accordance with the continuous change ofthe relative brightness. As a result, the user can easily recognize thedistribution of the relative brightness in the image region in thisrange.

If the pattern C is selected, the color conversion parameter generatingunit 107 determines the correspondence depicted in FIG. 8. In thecorrespondence in FIG. 8, a plurality of converted colors arecorresponded to a plurality of ranges (color conversion ranges) of thebrightness gradation values respectively. For example, a monochromecolor is corresponded to the color conversion range to which thebrightness gradation values in a 0 to 171 range belongs. Greencorresponds to a color conversion range that is within the brightnessgradation values 512 to 683.

In this way, if the pattern C is selected, the correspondence of theconverted color and the brightness gradation value is used, and thecolor conversion processing is performed based on the brightnessgradation value. Thereby the brightness gradation values (distributionof the brightness gradation values) of the input image data can beappropriately displayed by colors. As a result, the user can easilyrecognize the brightness gradation values of the input image data bycolors.

In a range (e.g. color conversion range), the brightness of theconverted color may continuously change in accordance with thecontinuous change of the brightness gradation values (brightness relatedvalues). Then in the image region in this range, gradation display canbe performed as the display of the converted colors, such that thebrightness of the converted colors continuously change in accordancewith the continuous change of the brightness gradation values. As aresult, the user can easily recognize the distribution of the relativebrightness in the image region in this range.

In the correspondences in FIG. 6A, FIG. 6B and FIG. 8, the non-colorconversion range is not set, instead a plurality of continuous colorconversion ranges are set, however the present invention is not limitedto this. For example, at least one of the case when the gradationcharacteristic of the input image data is gamma 2.2, and the case whenthe gradation characteristic of the input image data is Log, a pluralityof color conversion ranges, which are separated from each other, may beset. Further, in the case when the gradation characteristic of the inputimage data is ST 2084, a plurality of continuous color conversion rangesmay be set.

In the case when the gradation characteristic of the input image data isgamma 2.2, the specified display range (maximum value of a plurality ofbrightness gradation values belonging to the specified display range)may be determined. Then a converted color, which is different from aplurality of converted colors corresponding to a plurality of colorconversion ranges respectively, may be corresponded to the non-specifieddisplay range. In the non-specified display range, the brightness of theconverted color may continuously change in accordance with thecontinuous change of the brightness gradation values. In at least one ofthe case when the gradation characteristic of the input image data isgamma 2.2, and the case when the gradation characteristic of the inputimage data is ST 2084, the positions of the color conversion ranges, thewidth of each color conversion range and the like may depend on thespecified display range. Further, in at least one of the case when thegradation characteristic of the input image data is gamma 2.2, and thecase when the gradation characteristic of the input image data is Log,the positions of the color conversion ranges, the width of each colorconversion range and the like need not depend on the specified displayrange. Furthermore, in at least one of the case when the gradationcharacteristic of the input image data is gamma 2.2, and the case whenthe gradation characteristic of the input image data is Log, the numberof color conversion ranges and the like may depend on the specifieddisplay range.

A range of the brightness related values, which are lower than athreshold, may be set as the non-color conversion range. For example, inat least one of the case when the gradation characteristic of the inputimage data is ST 2084, and the case when the gradation characteristic ofthe input image data is Log, the range corresponding to SDR may be setas the non-color conversion range. In concrete terms, when the gradationcharacteristic of the input image data is ST 2084, the absolutebrightness in a 0 to 100 cd/m² range may be set as the non-colorconversion range corresponding to SDR. When the gradation characteristicof the input image data is Log, the relative brightness range in a 0% to100% range may be set as the non-color conversion range corresponding toSDR.

The color conversion parameter generating unit 107 may determine thenon-color conversion range, in accordance with the user operation to thedisplay apparatus 100 (image processing apparatus). For example, thecolor conversion parameter generating unit 107 may determine the abovementioned threshold in accordance with the user operation (secondthreshold determination processing). The user operation to determine thenon-color conversion range, the threshold and the like is a useroperation to specify the brightness related value, for example. In theuser operation to specify the brightness related value, the type of thebrightness related value is not especially limited. For example, theuser operation to specify the brightness gradation value may beperformed as the user operation to determine the non-color conversionrange, the threshold or the like, regardless the gradationcharacteristic of the input image data. However, in terms ofconvenience, it is preferable that the user operation to specify a typeof brightness gradation value in accordance with the gradationcharacteristic of the input image data is performed as the useroperation to determine the non-color conversion range, the threshold orthe like.

FIG. 7A to FIG. 7C are other examples of the correspondence of thepattern A. In the case of FIG. 7A, the specified display range includesall the absolute brightness values in a 0 to 10,000 cd/m² range definedin ST 2084. In the correspondence in FIG. 7A, a plurality of convertedcolors are corresponded to a plurality of ranges (color conversionranges) of the absolute brightness respectively. In the correspondenceof FIG. 7A, the converted color, of which brightness continuouslychanges in accordance with the continuous change of the absolutebrightness, is corresponded to each color conversion range. For example,a monochrome color, of which brightness continuously changes inaccordance with the continuous change of the absolute brightness, iscorresponded to the color conversion range to which the absolutebrightness in a 0 to 100 cd/m² range belongs. Green, of which brightnesscontinuously changes in accordance with the continuous change of theabsolute brightness, is corresponded to the color conversion range towhich the absolute brightness in a 400 to 1,000 cd/m² range belongs.Therefore in the image region in the color conversion range, gradationdisplay can be performed as the display of the converted colors, suchthat the brightness of the converted colors continuously change inaccordance with the continuous change of the absolute brightness.

In the case of FIG. 7B, the specified display range includes an absolutebrightness in a 0 to 1500 cd/m² range, and does not include the absolutebrightness higher than 1500 cd/m². The non-specifieddisplayrange is arange of the absolute brightness higher than 1500 cd/m². In thecorrespondence in FIG. 7B, the same settings as FIG. 7A (colorconversion ranges, correspondence between the color conversion range andthe converted color) are performed for the specified display ranges. Inother words, the position of each color conversion range does not dependon the specified display range, but is fixed, and the number of colorconversion ranges changes in accordance with the specified displayrange. A converted color, which is different from a plurality ofconverted colors corresponding to a plurality of color conversion rangesrespectively, is corresponded to the non-specified display range. Aconverted color, of which brightness continuously changes in accordancewith the continuous change of the absolute brightness, is correspondedto the non-specified display range as well. In concrete terms, red,which brightness continuously changes in accordance with the continuouschange of the absolute brightness, is corresponded to the non-specifieddisplay range.

In the case of FIG. 7C, the absolute brightness in a 0 to 100 cd/m²range is set as the non-color conversion range corresponding to SDR. Therest is the same as FIG. 7B. In other words, the position of each colorconversion range does not depend on the non-color conversion range,which is a range of the brightness related values that are lower thanthe threshold, but is fixed, and the number of color conversion rangeschanges in accordance with this non-color conversion range.

A correspondence using the relative brightness, instead of the absolutebrightness in FIG. 7A to FIG. 7C, may be used as the correspondence ofthe pattern B. A correspondence using the brightness gradation values,instead of the absolute brightness in FIG. 7A to FIG. 7C, may be used asthe correspondence of the pattern C.

As described above, according to this embodiment, the correspondence inaccordance with the gradation characteristic of the input image data isused as the correspondence between the brightness related value and theconverted color. Thereby the brightness distribution of the input imagedata can be displayed even more appropriately.

Each functional unit of this embodiment described above may or may notbe independent hardware. The functions of at least two functional unitsmay be implemented by common hardware. Each of a plurality of functionsof one functional unit may be implemented by independent hardware. Atleast two functions of one functional unit may be implemented by commonhardware. Each functional unit may or may not be implemented byhardware. For example, the apparatus may include a processor and amemory in which a control program is stored. Then the functions of atleast a part of the functional units of the apparatus may be implementedby the processor, which reads the control program from the memory, andexecutes the control program.

The above mentioned embodiment is merely an example, and a configurationthat can be implemented by appropriately modifying or changing theconfiguration of this embodiment, within the scope of the essentialcontent of the present invention, is also included in the presentinvention.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment (s) and/or controlling the one or more circuits to performthe functions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2017-038271, filed on Mar. 1, 2017, and Japanese Patent Application No.2017-228015, filed on Nov. 28, 2017, which are hereby incorporated byreference herein in their entirety.

What is claimed is:
 1. An image processing apparatus, comprising: aconverting unit configured to convert a color of input image data basedon information representing a correspondence between a brightness leveland a color, and generate converted image data; and a setting unitconfigured to set a gradation characteristic of the input image data,wherein the converting unit converts the color of the input image databased on information representing a first correspondence in a case wherethe gradation characteristic set by the setting unit is a firstgradation characteristic, and converts the color of the input image databased on information representing a second correspondence in a casewhere the gradation characteristic set by the setting unit is a secondgradation characteristic.
 2. The image processing apparatus according toclaim 1, wherein the setting unit sets the gradation characteristic inaccordance with an instruction inputted by the user.
 3. The imageprocessing apparatus according to claim 1, wherein the setting unit setsthe gradation characteristic based on meta data attached to the inputimage data.
 4. The image processing apparatus according to claim 1,wherein the information representing the correspondence is informationfor which a different color is corresponded to each of a plurality ofbrightness level ranges, and for each of the plurality of ranges, theconverting unit converts a color in a portion having a brightness levelin this range, out of the input image data, into a color which iscorresponded to this range in the information representing thecorrespondence.
 5. The image processing apparatus according to claim 1,wherein the first gradation characteristic is PQ defined in ST
 2084. 6.The image processing apparatus according to claim 1, wherein the secondgradation characteristic is a gradation characteristic in which arelative brightness level is corresponded to a gradation value.
 7. Theimage processing apparatus according to claim 1, wherein the convertingunit converts a color of a region, of which brightness level is a firstthreshold or less, out of the input image data, into monochrome.
 8. Theimage processing apparatus according to claim 1, further comprising agradation converting unit configured to convert the input image databased on the set gradation characteristic.
 9. The image processingapparatus according to claim 1, wherein the converting unit converts acolor of a region, of which brightness level is higher than a secondthreshold, out of the input image data, into a predetermined color. 10.The image processing apparatus according to claim 9, wherein the secondthreshold is a brightness level specified by the user.
 11. The imageprocessing apparatus according to claim 1, wherein the informationrepresenting the correspondence is information for which a differentcolor is corresponded to each of a plurality of sub-ranges constitutinga range of possible brightness levels of the input image data.
 12. Theimage processing apparatus according to claim 1, wherein the informationrepresenting the correspondence is information for which a differentcolor is corresponded to each of a plurality of boundary ranges whichrespectively include a plurality of boundaries of a plurality ofsub-regions constituting a range of possible brightness levels of theinput image data.
 13. The image processing apparatus according to claim1, wherein the first gradation characteristic is a gradationcharacteristic in which a value of a brightness level is corresponded toa gradation value of image data, and the second gradation characteristicis a gradation characteristic in which a brightness level is indirectlycorresponded to a gradation value of image data.
 14. An image processingmethod, comprising: a converting step of converting a color of inputimage data based on information representing a correspondence between abrightness level and a color, and generating converted image data; and asetting step of setting a gradation characteristic of the input imagedata, wherein in the converting step the color of the input image datais converted based on information representing a first correspondence ina case where the gradation characteristic set in the setting step is afirst gradation characteristic, and the color of the input image data isconverted based on information representing a second correspondence in acase where the gradation characteristic set in the setting step is asecond gradation characteristic.
 15. A non-transitory computer readablemedium that stores a program, wherein the program causes a computer toexecute: a converting step of converting a color of input image databased on information representing a correspondence between a brightnesslevel and a color, and generating converted image data; and a settingstep of setting a gradation characteristic of the input image data,wherein in the converting step the color of the input image data isconverted based on information representing a first correspondence in acase where the gradation characteristic set in the setting step is afirst gradation characteristic, and the color of the input image data isconverted based on information representing a second correspondence in acase where the gradation characteristic set in the setting step is asecond gradation characteristic.